Step 1

Preheat the oven to 425°F with a rack in the upper third position. Place a sturdy baking sheet in the oven to preheat with the oven. In a medium bowl, toss the sweet potatoes with the oil, thyme, and a generous pinch of salt and pepper. Line the preheated baking sheet with parchment (for easy clean up) and add the sweet potatoes in a single layer. Roast in the oven until nearly tender, about 10 minutes.

Step 2

While the sweet potatoes are roasting, combine the maple syrup, apple cider, apple cider vinegar, butter, and mustard in a small saucepan over medium-high heat and season with salt and pepper. Simmer until reduced to a thin syrup, 4 to 5 minutes.

Step 3

Remove the sweet potatoes from the oven and flip them over. Place the salmon, skin side down, on the baking sheet next to the sweet potatoes and brush with the maple-cider mixture. Transfer to the oven and roast until the sweet potatoes are tender and lightly browned and the salmon registers 125°F on an instant read thermometer, about 10 minutes, depending on thickness of the fillets. Remove the baking sheet from the oven and turn on the broiler.

Step 4

Return the baking sheet to the oven, and broil until lightly caramelized, 1 to 2 minutes. Watch carefully to avoid burning. Transfer the salmon and sweet potatoes to plates and serve.